"Having thus seen, what is imported in a Man's trusting his Heart."
(The end is a period, not a question mark.)
I wonder what it means.
"From what we have observed so far, what does 'one trusts one's
heart' mean?"???
Does 'Man's trusting his Heart' have a figurative meaning?

To "trust your heart" simply means to do what you feel is correct, or what your instincts tell you to do... in other words, don't use the brain too much! Of course it is figurative, because the heart doesn't really give advice, it just pumps blood.

[I think the poetry verse you quoted ended in a period rather than a question mark because it was the second half of a couplet that wasn't a question.]